New initialFile setting

Dromo now supports directly providing a file to the importer, bypassing the user selecting a file. The initialFile setting works similarly to the existing initialData setting, except instead of providing the parsed JSON, you simply provide the raw file which will be parsed by Dromo, just like a normal import.

This can be useful if you accept the file from a user elsewhere in your application and want to pass it on to Dromo, or if the file comes from some external source.